Developing Device and Process Cartridge and Imaged Forming Device Provided with them

ABSTRACT

Object: To prevent trailing and leading to enable excellent development with a simple constitution. 
     Solving Means: A maximum value F 0  of a magnetic attractive force near a main magnetic pole S 1  of magnetic poles formed by a magnetic field generating unit  3  of a developing apparatus  1  is positioned on a downstream side in a rotating direction of a developer carrier  2  beyond a peak position of a magnetic flux density in a normal line direction of the main magnetic pole S 1 , for example on the downstream side in the rotating direction of the developer carrier by at least 8° or more from the peak position of the magnetic flux density in the normal line direction of the main magnetic pole S 1 , and a half-value width of the maximum value F 0  of the magnetic attractive force has a narrow and peaked distribution of, for example, 54° or less.

TECHNICAL FIELD

The present invention relates to a developing apparatus and a processcartridge which are used in an image forming apparatus of anelectrophotographic system or an electrostatic recording system such asa copying machine or a page printer, and to an image forming apparatusincluding the developing apparatus and the process cartridge.

BACKGROUND ART

In an image forming apparatus using an electrophotographic system, anelectrostatic latent image formed on an image carrier is developed by adeveloping apparatus to be visualized, and as the developing apparatus,a developing apparatus using toner has been put in practical use widely.Like an LED or LBP printer, a recent image forming apparatus has becomean apparatus having a higher resolution, in association with which ahigher-resolution and high-definition developing system is required.

In order to realize high image quality, it is necessary to charge toner(developer) contained in a developing container of a developingapparatus sufficiently. This is because, when a Q/M [Q/M: toner chargeamount (μQ) per unit weight (g)] of toner on a developing sleeve issmall, toner scattering or a toner coat amount W is increased, so that achain-like particle cluster of toner at developing time becomes large,the particle cluster is fallen over and “trailing” is generated at atrailing end of an image, which degrades the image. Therefore, forexample, a thin-layer developing apparatus according to an elasticdeveloping blade method where a toner coat amount W [W: toner coatweight (mg) per square centimeter of a surface of a developing sleeve]on a developing sleeve (developer carrier) is reduced by causing adeveloping blade (developer restricting member) made of, for example, anelastic body to abut on the developing sleeve with a high pressure, andsimultaneously toner on the developing sleeve is applied with a largeQ/M has been developed conventionally.

However, when the developing blade made of an elastic body is caused toabut on the developing sleeve with a high pressure and the toner on thedeveloping sleeve is applied with a high Q/M, there is a problem thatmuch toner charged to reverse polarity is generated, which generates“leading” which means development of unnecessary toner at a leading endof the image. Moreover, even if the Q/M is made high so that a tonercoat amount is reduced, there is a problem that a chain-like particlecluster is fallen down due to difference in circumferential velocitybetween a paper and a photosensitive drum at a time of transferring,which generates trailing.

On the other hand, a magnet roller (magnetic field generating unit) forretaining/conveying toner (developer) is disposed in a fixed stateinside the above-described developing sleeve (developer carrier), butfor example in a developing apparatus disclosed in Patent Literature 1described below, such a configuration is made that an excellentdevelopment effect can be obtained by disposing a main magnetic pole ofplurality of magnetic poles provided on a magnet roller at a positioncorresponding to a developing region, and high image quality is attainedby setting magnetic flux density and a magnetic attractive force inaddition to magnetic flux density and a distribution thereof.

That is, in Patent Literature 1 described below, a maximum value F0 ofthe magnetic attractive force of the magnet roller is set in adownstream of a developing sleeve rotating direction beyond a peak of adeveloping pole S1, and a minimum value F2 is set near a peak positionof the developing pole S1, but in a distribution of the magneticattractive force at the case, there is a problem that an N1 pole and anN2 pole adjacent to the developing pole S1 make an influence, so thatthe respective magnetic poles are forced to be positioned so as toseparate from one another by about 90°, and application can be thereforeperformed to only a distribution of a magnetic flux density limited to acertain extent.

For example, recently, in an image forming apparatus whereprice-reduction and space-saving are attained by employing a verticalpaper path configuration where a paper is conveyed in a verticaldirection, instead of a horizontal path which has been usedconventionally, such a configuration has been adopted that aphotosensitive drum moves upwardly and the developing pole S1 and thedeveloping blade approaches to each other according to the vertical pathconfiguration, so that, when the S1 pole—the N1 pole is separated byabout 90° as described above, an N1 pole peak position is disposed at anip portion of the developing blade. That is, when the N1 pole peakposition is disposed at the nip portion of the developing blade, tonercoat on the developing sleeve becomes uneven, which may generate unevendensity, so that it is desired to displace the N1 pole so as to separatefrom the nip portion by at least about 30°, but when the N1 pole isdisplaced toward the S1 pole side by 30°, the N1 pole cannot bemagnetized sufficiently because the N1 pole is too close to the S1 pole.

Patent Literature 1: JP-B-07-066215

DISCLOSURE OF THE INVENTION Problem to be Solved by the Invention

Then, an object of the present invention is to provide a developingapparatus and a process cartridge where both trailing and leading areprevented to attain image quality improvement even in the developingapparatus of a thin-layer developing system where the respectivemagnetic poles of the magnetic roller cannot be disposed at intervals ofabout 90°.

Means for Solving the Problem

In order to attain the object, according to a first invention accordingto the present application, the object is attained by a developingapparatus comprising a developer carrier which is disposed opposite toan electrostatic latent image carrier and carries a developer to rotate,and a magnetic field generating unit which is fixedly disposed insidethe developer carrier and has a plurality of magnetic poles including amain magnetic pole positioned in a developing region, the main magneticpole of the magnetic field generating unit having a peak of magneticflux density in a normal line direction near a proximity position of theelectrostatic latent image carrier and the developer carrier and beingconfigured so as to generate a magnetic attractive force which is aresultant force of an attractive force based on the magnetic fluxdensity in the normal line direction and an attractive force based onmagnetic flux density in a tangential line direction on the developercarrier by the magnetic field generating unit, wherein a magnetizedpattern where a maximum value F0 of the magnetic attractive force F ispositioned on a downstream side in a rotating direction of the developercarrier beyond a peak position of the magnetic flux density in thenormal line direction of the main magnetic pole, and a half-value widthof the maximum value F0 of the magnetic attractive force becomes smallerthan that of the magnetic flux density in the normal line direction inthe main magnetic pole is applied to the magnetic field generating unit.

According to a second invention according to the present application,the object is attained by adopting such a constitution that developerhas a weight average particle diameter of 3.0 to 7.2 μm and an MI valueof 3 to 30 g/10 min and a developer amount W [W: toner coat amount (mg)per square centimeter of a surface of the developer carrier] layered onthe above-described developer carrier satisfies 0.6≦W≦1.5, or adoptingsuch a constitution that the maximum value F0 of the above-describedmagnetic attractive force is positioned on the downstream side by atleast 8° or more in the rotating direction of the developer carrier fromthe peak position of the magnetic flux density in the normal linedirection of the main magnetic pole and a half-value width of themaximum value F0 of the above-described magnetic attractive force has adistribution within a range of 54° or less, or adopting such aconstitution that a 90% width of the maximum value F0 of theabove-described magnetic attractive force is set to 20° or less.

According to a third invention according to the present application, theobject is attained by a process cartridge configured by arranging eitherone or more than one of an electrostatic latent image carrier, acharging device, a transferring device, and a cleaner, and a developingapparatus in a casing attachably and detachably accommodated in an imageforming apparatus, the developing apparatus comprising a rotatabledeveloper carrier, a magnetic field generating unit which is fixedlydisposed inside the developer carrier and has a plurality of magneticpoles including a main magnetic pole positioned in a developing region,a developer restricting member abutting on the developer carrier, and adeveloping container containing developer supplied to the developercarrier, where the developer has a weight average particle diameter of3.0 to 7.2 μm and an MI value of 3 to 30 g/10 min, and a developeramount W [W: toner coat amount (mg) per square centimeter of a surfaceof the developer carrier] layered on the developer carrier satisfies0.6≦W≦1.5, wherein the main magnetic pole has a peak of magnetic fluxdensity in a normal line direction at a proximity position of theelectrostatic latent image carrier and the developer carrier, generatesa magnetic attractive force which is a resultant force of an attractiveforce based on the magnetic flux density in the normal line directionand an attractive force based on a magnetic flux density in a tangentialline direction on the developer carrier by the magnetic field generatingunit, a maximum value F0 of the magnetic attractive force is positionedon a downstream side in a rotating direction of the developer carrier byat least 8° or more from the peak position of the magnetic flux densityin the normal line direction of the main magnetic pole, and a half-valuewidth of the maximum value F0 of the magnetic attractive force has adistribution of 54° or less.

According to a fourth invention according to the present application,the object is attained by setting a 90% width of the maximum value F0 ofthe magnetic attractive force to 20° or less.

According to a fifth invention according to the present application, theabove-described object is attained by an image forming apparatus whereinthe developing apparatus or the process cartridge in either one of therespective inventions described above is provided.

EFFECT OF THE INVENTION

As described above, according to the first, the second, the fourth, orthe fifth invention according to the present application, since themaximum value F0 of the magnetic attractive force near the main magneticpole of the magnetic poles formed by the magnetic field generating unitof the developing apparatus is positioned on the downstream side in therotating direction of the developer carrier beyond the peak position ofthe magnetic flux density in the normal line direction of the mainmagnetic pole, for example on the downstream side in the rotatingdirection of the developer carrier by at least 8° or more from the peakposition of the magnetic flux density in the normal line direction ofthe main magnetic pole, and the half-value width of the maximum value F0of the magnetic attractive force has a narrow and peaked distributionof, for example, 54° or less, trailing and leading are prevented and anexcellent development can be performed.

According to the third, the fourth or the fifth invention according tothe present application, in the process cartridge where either one ormore than one of the electrostatic latent image carrier, the chargingdevice, the transferring device, and the cleaner, and the developingapparatus are disposed in the casing and integrated therewith, and thecasing is configured so as to be attachable to/detachable from the imageforming apparatus main body, since the magnetic field generating unitused in the first and second inventions are used as a magnetic fieldgenerating unit used in the developing apparatus in the cartridge, aneffect of preventing trailing and leading and performing an excellentdevelopment owing to the first and the second inventions can beobtained, and it becomes possible to exchange these components easily,so that maintenance easiness of the image forming apparatus can beimproved.

BEST MODE FOR CARRYING OUT THE INVENTION

Embodiments of the present invention will be explained below in detailwith reference to the drawings.

A developing apparatus 1 of a first embodiment according to the presentinvention shown in FIG. 1 is used in an image forming apparatus such asa laser printer, and it is provided with a function of developing anelectrostatic latent image formed on a surface of a photosensitive drum11 serving as an electrostatic latent image carrier.

A developing sleeve 2 serving as a developer carrier disposed oppositeto the photosensitive drum 11 which is the above-described electrostaticlatent image carrier is disposed inside the developing apparatus 1, anda magnet roller 3 serving as a developer carrier is fixedly disposed inthe developing sleeve 2. A developing blade 4 serving as a developeramount restricting member for restricting a developer amount is disposedon a surface of the developing sleeve 2 so as to abut on a predeterminedposition, and only an appropriate amount of toner (not shown) serving asmagnetic developer for visualizing an electrostatic latent image ischarged from a toner supplying port 5 a of a developing hopper 5 whichis a developing container and contained in the developing hopper 5.

For the magnetic developer in the embodiment, the following negativeelectric magnetic monocomponent toner is used, for example. That is,such toner is employed that is obtained by melting and kneading 100weight parts of styrene n-butyl acrylate copolymer as binder resin, and80 weight parts of magnetic particle, 2 weight parts of negative chargecontrol agent of monoazo iron complex, and 3 weight parts of low mol.wt. polypropylene as wax by a biaxial extruder heated to 140° C.,coarsely crushing the cooled-down kneaded mixture by a hammer mill,finely pulverizing the coarsely-crushed material by a jet mill, andair-classifying the obtained pulverized material to obtain a classifiedpowder having a weight average diameter of 5.0 μm, and then, mixing 1.0weight part of hydrophobic silica fine powder to the classified materialwhich has an average particle diameter of 5.0 μm by a Henschel mixer.

A melt index (MI) which is a fixing index of the toner indicates 20 g/10min, for example. Measuring the melt index (MI) is performed using anapparatus (an apparatus used in a flow test method for thermoplastic)described in JISK7210, and measuring conditions at the time are, forexample, as follows:

Under a condition that as a measurement temperature is 125° C., a loadis 5 kg, and a sample filling amount is in a range of 5 to 10 g,measurement is performed by a manually cutting method, and the measuredvalue at that time is converted to a 10-min value. For measuring anaverage particle diameter of the toner, a Coulter Multisizer II (made byBECKMAN COULTER, Inc.) is used to obtain a weight average particlediameter D4 (μm) based on weight from a volume distribution of thetoner. Incidentally, as a toner of the developing apparatus of theembodiment, a toner having an MI of 3 to 30 g/10 min and a weightaverage particle diameter of 3.0 to 7.2 μm can be used.

A sleeve which is a nonmagnetic aluminum sleeve with a diameter of φ16.0whose surface roughness Ra=1.0 μm is coated with a resin layercontaining conductive particles is used for the developing sleeve 2disposed opposite to the above-described photosensitive drum 11, and thesleeve can rotate in a counterclockwise direction to convey the toner ina direction toward the photosensitive drum 11. The developing sleeve 2and the photosensitive drum 11 are opposed to each other and there is agap of 300 μm between them at a closest position. The magnet roller 3fixedly disposed in the developing sleeve 2 can form magnetic fields atleast four portions of an N1 pole, an S2 pole, an N2 pole, and an S1pole on the developing sleeve 2, respectively. An arrangementrelationship of these magnetic poles will be described later.

Further, the developing blade 4 abutting on the developing sleeve 2 torestrict a developer amount is formed from, for example, silicon rubberhaving rubber hardness degree of 40° (JISA), and by causing an endportion of the developing blade 4 to abut on a surface of the developingsleeve 2 at a predetermined position, a toner layer having a uniformthickness can be formed on the surface of the developing sleeve on adownstream side in a rotating direction thereof beyond a position of thedeveloping sleeve 4.

At this time, an abutting force P [P: abutting load (gf) per unit length(1 cm) in a longitudinal direction of the developing sleeve] appliedwhen the developing blade 4 abuts on the developing sleeve 2 is set toabout 30 gf/cm. An abutting width (nip) of the developing sleeve 2 andthe developing blade 4 is set to 1.0 mm, and a distance from anuppermost-stream position to the rotating direction of the developingsleeve to a free end of the developing blade is set to 2.0 mm. Adeveloper amount (toner coat amount) W on the developing sleeve 2 undersuch conditions becomes about 1.30 (mg/cm²).

A rotary T stirring rod 6 and a rotary D stirring rod 7 are disposed inthe developing hopper 5 containing the toner and near the developingsleeve 2, and such a configuration is adopted that the toners in thedeveloping hopper 5 and near the developing sleeve 2 are stirred by boththe stirring rods 6 and 7, and the toner in the developing hopper 5 issupplied in a direction of the developing sleeve 2. A conductivedetecting member 8 for remaining toner amount detection is provided nearthe developing sleeve 2, so that a remaining toner amount can bedetected to replenish toner at an appropriate time.

Then, after sent near the developing sleeve 2 by the T stirring rod 6and the D stirring rod 7, monocomponent magnetic toner in theabove-described developing hopper 5 is supplied to the developing sleeve2 by the action of magnetic field formed by the magnetic roller 3, andconveyed in the photosensitive drum direction 11 according to rotationof the developing sleeve 2 (which rotates in a counterclockwisedirection). Thereafter, the monocomponent magnetic toner is subjected tocharge application and layer thickness restriction at an abuttingportion of the developing sleeve 2 and the developing blade 4 and isconveyed to a developing region formed by the developing sleeve 2 andthe photosensitive drum 11.

When a electrostatic latent image on the surface of the photosensitivedrum 11 is developed by a developing apparatus having such aconfiguration, an alternating voltage obtained by superimposing analternating current on a direct current is applied on the developingsleeve 2 from a bias supply (not shown) to form a development electricfield between the developing sleeve 2 and the photosensitive drum 11,and development of an electrostatic latent image is performed by theelectric field. A developing bias obtained by superimposing an AC(rectangular wave Vpp=1600V, f=2400 Hz) on a direct-current voltage(Vdc=−500V) is applied to the developing sleeve 2 at this time. Thephotosensitive drum 11 is uniformly charged to charged potentialVd=−700V by a charging device (not shown) and is thereafter exposed by alaser according to an image signal, so that an electrostatic latentimage is formed on the surface of the photosensitive drum 11(Incidentally, the exposed portion becomes Vl=−150V). The exposed Vlportion is reversely developed with negatively charged toner by thedeveloping apparatus to develop the electrostatic latent image.

Here, the above-described magnet roller 3 is configured so as togenerate a magnetic attractive force which is a resultant force of anattractive force based on a magnetic flux density of a normal linedirection and an attractive force based on a magnetic flux density of atangential line direction on the developing sleeve 2 by the magnetroller 3, and in particular a main magnetic pole S1 is disposed so as tohave a peak of the magnetic flux density of the normal line directionnear the closest position of the developing sleeve 2 and thephotosensitive drum 11.

A magnetic attractive force pattern of the magnet roller 3 is as shownin FIG. 2, for example. That is, in FIG. 2, a magnetic flux densitypattern in the normal line direction of the magnet roller 3 is shown bya thick solid line, and a magnetic attractive force pattern is shown bya thin solid line in the first embodiment of the present invention. Amagnetic flux density pattern in a normal line direction is shown by athick broken line and a magnetic attractive force pattern is shown by athin broken line in the conventional magnet roller. In FIG. 8, only themagnetic attractive force pattern in the first embodiment of the presentinvention is extracted and shown.

As understood from FIG. 2 and FIG. 8, in the magnet roller 3 used in thefirst embodiment, when compared with the conventional magnet roller, amaximum value F0 of the magnetic attractive force is positioned on adownstream side in a rotating direction of the developing sleeveindicated by an arrow beyond a peak angular position of the mainmagnetic pole S1, and the pattern has a peaked waveform shape. A minimumvalue F2 of the magnetic attractive force is constituted so as not to bepresent near the center of the peak angle of the S1 pole of the mainmagnetic pole.

More particularly, the maximum value F0 of the magnetic attractive forceis positioned on the downstream side by at least 8° or more from a peakposition of the magnetic flux density in the normal line direction ofthe main magnetic pole S1, and a half-value width of the maximum valueF0 of the magnetic attractive force has a peaked distribution of 54° orless and 90% width of the maximum value F0 of the magnetic attractiveforce is set to 20° or less. Incidentally, the above-describedhalf-value width of the magnetic attractive force is also called 50%width, and expressed by a central angle at a position where a value ofthe magnetic attractive force is a half (50%) value of a peak value inthe normal line direction. Therefore, 90% width means a central angle ina position where a value of the magnetic attractive force is a 90% valueof the peak value in the normal line direction.

Regarding such a configuration, the present inventor(s) has observed“trailing” and “leading” when the magnet of the embodiment is used andwhen the conventional magnet is used, as shown in the following table 1.That is, a relationship among an angle, a peak value, and a value of ahalf value width of the magnetic attractive force F obtained when themagnetic attractive force patterns shown in FIG. 2 to FIG. 7 are swung,a trailing index, and leading generation Vback is shown in the followingtable 1.

TABLE 1 Angle of magnetic attractive force F0 (degree on downstreamhalf-value side width of beyond S1 magnetic magnetic leading Magnet polepeak attractive attractive trailing generation roller angle) force F0force F0 index Vback[V] Conventional 0° 1.13 nN 66° 35.5 −160 magnetSame as S1 pole peak First 8° 2.05 nN 41° 9.7 −215 Embodiment downstreamSecond 9° 1.70 nN 54° 15.2 −210 Embodiment downstream Comparative 6°1.67 nN 49° 41.8 −175 example 1 downstream Comparative 1° 1.67 nN 103° 46.7 −205 example 2 downstream

The trailing index at this time is obtained by measuring an area oftrailing and multiplying the area by a coefficient according to thearea, where a bigger index shows a worse trailing, and a smaller indexshows a better trailing. The leading generation Vback is a contrastwhere occurrence of leading starts, and wider latitude can be takenaccording to increase of a minus figure of the leading generation Vback.Incidentally, the half-value width of the magnetic attractive force isshown by a value of an angle (elevation angle) formed by a lineconnecting a point on the developing sleeve in the maximum value of amagnetic attractive force line and two points which are a ½ value of themaximum value F0 of the magnetic attractive force.

As apparent from the above table 1, FIG. 4, and FIG. 8, the magnetroller in the embodiment 1 of the present invention shows a narrow andpeaked waveform shape such that the maximum value F0 of the magneticattractive force near the main magnetic pole S1 is positioned on thedownstream side by 8° from the peak angle of the main magnetic pole S1,the half-value width is 41°, and the 90% width is 12°. Thus the trailingindex is 9.7, which is improved largely as compared with theconventional magnet. In the leading generation Vback, the latitudebecomes wider by 55V.

On the contrary, a magnet roller in the comparative example 1 shows apeaked waveform shape such that the maximum value F0 of the magneticattractive force is positioned on an upstream side by 6° from the S1pole peak angle and the half-value width is 49° but the trailing indexis 41.8, which is a bad result. The leading generation Vback is improvedby latitude of 15V. As understood from this result, it has beenunderstood that, when the magnetic attractive force is set on anupstream side, image quality degrades and leading latitude is notimproved so much.

A magnet roller in the comparative example 2 shows a broad waveformshape such that the maximum value F0 of the magnetic attractive force ispositioned on an upstream side by 1° from the 51 pole peak angle, andthe half-value width is 103°. As compared with the conventional magnetroller, the trailing index gets worse largely. However, the leadinglatitude becomes wider by 45 V. As understood from the result, it hasbeen understood that, when the half-value width of the magneticattractive force F is made wide to have a broad waveform shape, theleading latitude becomes wider, but trailing gets worse.

Further, as apparent from the above-described table 1 and FIG. 5, asecond embodiment according to the present invention shows a broadwaveform such that the half-value width is 54° and 90% width is 17°,which is slightly wider than a magnetic attractive force waveform of thefirst embodiment, but a position of the magnetic attractive force F isset in downstream by 9°. It is understood that the trailing index is15.2 and such a wide leading generation Vback as −210 V can be taken,which is not so much as the magnet roller of the first embodiment.

From such results of the first and second embodiments and thecomparative examples 1 and 2, when the magnet roller is set such thatthe magnetic attractive force F0 is set on a downstream side by at least8° or more from the S1 pole peak angle, and the half-value width of themagnetic attractive force F is set to 54° or less, an excellent magnetroller which satisfies both trailing and leading can be obtained. As canbe understood from the above result, the minimum magnetic attractiveforce F2 is not necessarily positioned near the S1 pole peak angle.

On the other hand, in a third embodiment of the present invention shownin FIG. 9, the developing apparatus is disposed in a process cartridge20 which can be attachably and detachably accommodated in the imageforming apparatus main body, and such a configuration is adopted thateither one or a combination of at least two of the above-describedphotosensitive drum 11, a charging device 21 as a process unit acting onthe photosensitive drum 11, a cleaning device 24, and a waste tonercontainer 23 containing a cleaned developer, and the developingapparatus described in the above-described first or second embodimentare respectively disposed in the process cartridge 20.

More particularly, in the process cartridge 20 attachably and detachablyaccommodated in the image forming apparatus, the photosensitive drum 11is disposed near an opening portion in a casing which can be containedin the image forming apparatus, and the developing apparatus 1 whichdevelops an electrostatic latent image on the photosensitive drum 11 isdisposed at a position opposite to the photosensitive drum 11. Thedeveloping apparatus 1 is the same as in the above-described firstembodiment, the developing sleeve 2 is disposed at a position oppositeto the photosensitive drum 11, the developing blade 4 is disposed suchthat an end portion of the developing blade 4 abuts on the surface ofthe developing sleeve 2, and the developing hopper 5 is disposed so asto be capable of supplying toner near the developing sleeve 2.

The cleaning device 24 having a cleaning blade 22 is disposed in thecasing on the side opposite to the developing apparatus side of thephotosensitive drum 11, and residual toner adhered on the surface of thephotosensitive drum 11 after transferring step is scrapped off by thecleaning blade 22 and can be received in the waste toner container 23 ofthe cleaning device 24. The process cartridge 20 is configured such thatthe charging device 21 which charges the photosensitive drum 11 isdisposed in the casing on an upstream side in the rotating direction ofthe photosensitive drum 11 beyond the developing sleeve 2 and before thecleaning device 24. Incidentally, either one or a combination of atleast two of the photosensitive drum 11, the charging device 21, thecleaning device 24 and the waste toner container 23, and the developingapparatus may be combined to be contained in the casing of the processcartridge.

Incidentally, the same magnet roller 3 as used in the first embodimentis fixedly disposed inside the above-described developing sleeve 2, theN1 pole, the S1 pole, the N2 pole, and the S2 pole can be respectivelyformed on the surface of the developing sleeve 2 by the magnet roller 3according to the same positional relationship in the first embodiment,and values of an angle and a half-value width of the magnetic attractiveforce F become the same values in the first embodiment. Incidentally, asa magnet roller, the magnet roller used in the second embodiment canalso be used.

The process cartridge 20 having the configuration is set at apredetermined position of the image forming apparatus and can performimage formation in a predetermined process, and when reaching the end ofits life due to consumption of toner or wearing of members in thecartridge, the process cartridge 20 can be exchanged with a new processcartridge to perform high-quality-image formation continuously.

Since an integrated process cartridge is made by disposing thedeveloping apparatus having the developing sleeve 2, the developingblade 4 and the like, the photosensitive drum 11, the charging device21, and the cleaning device 24 in the casing which can be accommodatedin the image forming apparatus in this manner, such an effect explainedin the first and second embodiments can be obtained that trailing andleading are prevented and excellent image formation can be performed,and additionally, exchange of each component in the cartridge and awaste toner processing can be performed easily without makingsurroundings dirty with toner. Therefore, maintenance easiness of theimage forming apparatus can be improved dramatically, and since aprincipal component in an electrophotographic system is exchanged with anew one by exchanging the cartridge, a high-quality image can bemaintained constantly and easily.

The embodiments of the invention which has been made by the presentinventor(s) have been specifically explained above, but it is obviousthat the present invention is not limited to the embodiments, and can bemodified variously without departing from the scope of the presentinvention.

For example, the above-described embodiments of the present inventioncan be applied similarly to another image forming apparatus such as acopying machine except for a printer.

INDUSTRIAL APPLICABILITY

The above-described image forming apparatus according to the presentinvention can be widely applied to various image forming apparatusessuch as a copying machine, including an image forming apparatus such asa printer.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a sectional schematic view of a developing apparatus accordingto an embodiment of the present invention;

FIG. 2 is an explanatory diagram showing a relationship between amagnetic flux density pattern and a magnetic attractive force pattern ina magnet roller;

FIG. 3 is an explanatory diagram showing a magnetic flux density in anormal line direction and a magnetic attractive force of a conventionalmagnet roller;

FIG. 4 is an explanatory diagram showing a magnetic flux density in anormal line direction and a magnetic attractive force of a magnet rollerof a first embodiment;

FIG. 5 is an explanatory diagram showing a magnetic flux density in anormal line direction and a magnetic attractive force of a magnet rollerof a second embodiment;

FIG. 6 is an explanatory diagram showing a magnetic flux density in anormal line direction and a magnetic attractive force of a magnet rollerof a comparative example 1;

FIG. 7 is an explanatory diagram showing a magnetic flux density in anormal line direction and a magnetic attractive force of a magnet rollerof a comparative example 2;

FIG. 8 is an explanatory diagram of the magnetic attractive forcepattern in the magnet roller extracted from the first embodiment of thepresent invention shown in FIG. 2 to be shown; and

FIG. 9 is a sectional schematic view showing a process cartridgeaccording to a third embodiment.

EXPLANATION OF REFERENCE NUMERALS

-   1 developing apparatus-   2 developing sleeve (developer carrier)-   3 magnet roller (magnetic field generating unit)-   4 developing blade (developer restricting member)-   5 developing hopper-   6 T stirring rod-   7 D stirring rod-   8 remaining toner amount detecting member-   11 photosensitive drum (electrostatic latent image carrier)-   20 process cartridge-   21 charging device-   24 cleaning device

1. A developing apparatus comprising a developer carrier which isdisposed opposite to an electrostatic latent image carrier and carries adeveloper to rotate, and a magnetic field generating unit which isfixedly disposed inside the developer carrier and has a plurality ofmagnetic poles including a main magnetic pole positioned in a developingregion, the main magnetic pole of the above-described magnetic fieldgenerating unit having a peak of magnetic flux density in a normal linedirection near a proximity position of the electrostatic latent imagecarrier and the developer carrier, and being configured so as togenerate a magnetic attractive force which is a resultant force of anattractive force based on the magnetic flux density in the normal linedirection and an attractive force based on magnetic flux density in atangential line direction on the developer carrier by the magnetic fieldgenerating unit, wherein a magnetized pattern where a maximum value F0of the magnetic attractive force F is positioned on a downstream side ina rotating direction of the above-described developer carrier from apeak position of the magnetic flux density in the normal line directionof the main magnetic pole, and a half-value width of the maximum valueF0 of the magnetic attractive force becomes smaller than that of themagnetic flux density in the normal line direction in the main magneticpole is applied to the magnetic field generating unit.
 2. The developingapparatus according to claim 1, wherein the developer have a weightaverage particle diameter of 3.0 to 7.2 μm and an MI value of 3 to 30g/10 min, and a developer amount W [W: toner coat amount (mg) per squarecentimeter of a surface of the developer carrier] layered on thedeveloper carrier satisfies 0.6≦W≦1.5.
 3. The developing apparatusaccording to claim 1 or 2, wherein the maximum value F0 of the magneticattractive force is positioned on the downstream side by at least 8° ormore in the rotating direction of the developer carrier from the peakposition of the magnetic flux density in the normal line direction ofthe main magnetic pole, and a half-value width of the maximum value F0of the magnetic attractive force has a distribution within a range of54° or less.
 4. The developing apparatus according to any one of claims1 to 3, wherein a 90% width of the maximum value F0 of the magneticattractive force is set to 20° or less.
 5. A process cartridgeconfigured with either one or more than one of an electrostatic latentimage carrier, a charging device, a transferring device, and a cleaner,and a developing apparatus which are disposed in a casing attachably anddetachably accommodated in an image forming apparatus main body, thedeveloping apparatus comprising a rotatable developer carrier, amagnetic field generating unit which is fixedly disposed inside thedeveloper carrier and has a plurality of magnetic poles including a mainmagnetic pole positioned in a developing region, a developer restrictingmember abutting on the developer carrier, and a developing containercontaining a developer supplied to the developer carrier, the developerhaving a weight average particle diameter of 3.0 to 7.2 μm and an MIvalue of 3 to 30 g/10 min, and a developer amount W [W: toner coatamount (mg) per square centimeter of a surface of the developer carrier]layered on the developer carrier satisfying 0.6≦W≦1.5, wherein the mainmagnetic pole has a peak of magnetic flux density in a normal linedirection at a proximity position of the electrostatic latent imagecarrier and the developer carrier, the magnetic field generating unitgenerates a magnetic attractive force which is a resultant force of anattractive force based on the magnetic flux density in the normal linedirection and an attractive force based on magnetic flux density in atangential line direction on the developer carrier, a maximum value F0of the magnetic attractive force is positioned on a downstream side in arotating direction of the developer carrier by at least 8° or more fromthe peak position of the magnetic flux density in the normal linedirection of the main magnetic pole, and a half-value width of themaximum value F0 of the magnetic attractive force has a distribution of54° or less.
 6. The process cartridge according to claim 5, wherein a90% width of the maximum value F0 of the magnetic attractive force isset to 20° or less.
 7. An image forming apparatus wherein a developingapparatus according to any one of claims 1 to 4, or a process cartridgeaccording to claim 5 or 6 is provided.